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Full Discussion: File Descriptors + cron
Top Forums UNIX for Advanced & Expert Users File Descriptors + cron Post 302118541 by Perderabo on Tuesday 22nd of May 2007 07:06:01 PM
Old 05-22-2007
The exact particulars vary depending on OS. I will use HP-UX as an example. The number of possible file decriptors is under the control of setrlimit(2). (A less powerful interface, ulimit() is also available.) A process cannot have more fd's than the "soft" limit . Using setrlimit(2), a process may raise or lower its soft limit. But a process cannot raise the soft limit above the hard limit. A process can lower the hard limit. Only a root process can raise the hard limit. Kernel parameters define the initial value of the hard and soft limit. Even root cannot raise the hard limit above the initial value for the hard limit. The kernel paramters:
maxfiles
maxfiles_lim

I have cheated a little bit by picking HP-UX as my sample OS. HP-UX allows dynamic reconfiguration of the kernel. Only root can reconfigure the kernel. But a root process could, in theory, raise maxfiles_lim and then raise its hard limit and then relower maxfiles_lim. Not all versions of Unix give that much power to a root process.

I don't believe that cron fiddles with these limits.
 

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plimit(1)							   User Commands							 plimit(1)

NAME
plimit - get or set the resource limits of running processes SYNOPSIS
plimit [-km] pid... plimit {-cdfnstv} soft,hard... pid... DESCRIPTION
If one or more of the cdfnstv options is specified, plimit sets the soft (current) limit and/or the hard (maximum) limit of the indicated resource(s) in the processes identified by the process-ID list, pid. Otherwise plimit reports the resource limits of the processes identi- fied by the process-ID list, pid. Only the owner of a process or the super-user is permitted either to get or to set the resource limits of a process. Only the super-user can increase the hard limit. OPTIONS
The following options are supported: -k On output, show file sizes in kilobytes (1024 bytes) rather than in 512-byte blocks. -m On output, show file and memory sizes in megabytes (1024*1024 bytes). The remainder of the options are used to change specified resource limits. They each accept an argument of the form: soft,hard where soft specifies the soft (current) limit and hard specifies the hard (maximum) limit. If the hard limit is not specified, the comma may be omitted. If the soft limit is an empty string, only the hard limit is set. Each limit is either the literal string unlimited, or a number, with an optional scaling factor, as follows: nk n kilobytes nm n megabytes (minutes for CPU time) nh n hours (for CPU time only) mm:ss minutes and seconds (for CPU time only) The soft limit cannot exceed the hard limit. -c soft,hard Set core file size limits (default unit is 512-byte blocks). -d soft,hard Set data segment (heap) size limits (default unit is kilobytes). -f soft,hard Set file size limits (default unit is 512-byte blocks). -n soft,hard Set file descriptor limits (no default unit). -s soft,hard Set stack segment size limits (default unit is kilobytes). -t soft,hard Set CPU time limits (default unit is seconds). -v soft,hard Set virtual memory size limits (default unit is kilobytes). OPERANDS
The following operands are supported. pid Process ID list. EXIT STATUS
plimit returns the exit value zero on success, non-zero on failure (such as no such process, permission denied, or invalid option). FILES
/proc/pid/* process information and control files ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWesu | +-----------------------------+-----------------------------+ SEE ALSO
ulimit(1), proc(1), getrlimit(2), setrlimit(2), proc(4), attributes(5), SunOS 5.10 8 Jun 1998 plimit(1)
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